1. Field of the Invention
The present invention relates to a writable information recording medium, and more particularly, to a writable information recording medium capable of being played back with a commercially available laser disk player, for example a compatible information recording medium to a laser disk (hereinafter "LD") capable of recording the analogue signal.
2. Description of the Related Art
There is an optical disk so-called Compact Disk (hereinafter "CD") widely used as a Read Only Memory (hereinafter "ROM") medium on which data has been prerecorded in the fields of audio recording and information processing. In the CD, pre-pits corresponding to data to be reproduced have previously been formed on a plastic substrate by an injection molding, and a reflective layer is formed on the pits-formed substrate, with a protective layer covering the top of the reflective layer. There are specifications for recording and reading some digital signals for this CD which is standardized and so called CD specifications. CD players, which conform to the CD specifications, are widely used as CD reproducing apparatuses, although this type of medium is no writable.
There is an optical disk on which pits are written once which is so-called CD-R capable of being used directly in available CD players aforementioned. This writable CD-R comprises an optical absorbing layer absorbing light formed on a plastic substrate with a 12 cm diameter, and a reflective layer is formed on the substrate. In the conventional CD-R, a cyanine dye is used for the absorbing layer and gold (Au) is used for the reflective layer. The digital signal is recorded for an audio signal in the CD-R.
On the other hand, there is no LD with a 30 or 20 cm diameter having an absorbing layer for recording pits on which an analog signal frequency-modulated for an audio signal is recorded, that is, a writable LD or recordable laser disk (LD-R) does not exist. There is therefore a strong demand for the development of such a writable LD or recordable laser disk, which conforms to the standards of the LD specifications and can be thus used directly in available LD players as in the similar manner of that of the CD-R.
However, in case that an analogue signal is recorded by using a semiconductor laser to an LD type optical disk having a recording layer or an optical absorbing layer made of the cyanine dye as used in CD-R, it is difficult to record pits on the optical absorbing layer because insufficiency of sensitivity of the optical absorbing layer at a high linear velocity rotation higher than that of a CD type optical disk. As a result, such an analogue signal recording in the LD type medium is not practical. Furthermore, a digital signal is recorded on the CD-R under the generous conditions of jitter in the CD specifications, but the analogue signal is recorded onto an LD type optical disk in the LD specifications. Therefore, influence of jitter or the like becomes serious in the LD type optical disk. Such an LD utilizing the cyanine dye for the absorbing layer does not fit to a practical usage of recording and reproducing for an analogue video signal.